The present invention generally relates to fuel-fired heating appliances and, in a preferred embodiment thereof, more particularly provides a gas-fired water heater having incorporated therein a specially designed combustion air shutoff system.
Gas-fired residential and commercial water heaters are generally formed to include a vertical cylindrical water storage tank with a gas burner disposed in a combustion chamber below the tank. The burner is supplied with a fuel gas through a gas supply line, and combustion air through an air inlet flow path providing communication between the exterior of the water heater and the interior of the combustion chamber.
Water heaters of this general type are extremely safe and quite reliable in operation. However, under certain operational conditions the temperature and carbon monoxide levels within the combustion chamber may begin to rise toward undesirable magnitudes. Accordingly, it would be desirable, from an improved overall control standpoint, to incorporate in this type of fuel-fired water heater a system for sensing these operational conditions and responsively terminating the firing of the water heater. It is to this goal that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, fuel-fired heating apparatus is provided which is representatively in the form of a gas-fired water heater and includes a combustion chamber thermally communicatable with a fluid to be heated, and a burner structure associated with the combustion chamber and operative to receive fuel from a source thereof. A wall structure defines a flow path through which combustion air may flow into the combustion chamber for mixture and combustion with fuel received by the burner structure to create hot combustion products within the combustion chamber.
The water heater also incorporates therein a specially designed combustion air shutoff system, operative in response to an increased combustion temperature within the combustion chamber created by a reduction in the quantity of combustion air entering the combustion chamber via the flow path (caused, for example, by a progressive clogging of the flow path), for terminating combustion air supply to the combustion chamber, to thus terminate firing of the burner structure, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide therein. Representatively, this predetermined elevated concentration of carbon monoxide is in the range of from about 20 ppm to about 400 ppm by volume.
According to one aspect of the invention in a preferred embodiment thereof, the burner structure is disposed within the combustion chamber, a bottom wall of the combustion chamber is defined by an arrestor plate having a perforated portion defined by a series of flame quenching openings extending through the plate, and the combustion air shutoff system includes a heat-frangible temperature sensing structure extending through the arrestor plate into the interior of the combustion chamber, preferably adjacent the burner structure therein. The temperature sensing structure functions to sense a predetermined, undesirably elevated combustion temperature within the combustion chamber, which may be caused by a reduction in the quantity of air being delivered to the combustion chamber via the flow path, or by burning in the combustion chamber of extraneous flammable vapor which has entered its interior through the arrestor plate flame quenching openings, and responsively activate the balance of the combustion air shutoff system to terminate further air inflow into the combustion chamber.
In a preferred embodiment thereof, the temperature sensing structure includes a base frame member having a base wall secured to the inner side of the arrestor plate and having an opening extending therethrough which is aligned with a corresponding rod opening in the arrestor plate. A support frame member is releasably secured to the base frame member, preferably by a twist lock interconnection therebetween, and has spaced apart opposing first and second wall portions, the first wall portion having an opening therewith which overlies the base wall opening of the base frame member.
A heat-frangible element, preferably a fluid-filled glass bulb, is releasably carried by the support frame member and bears against its second wall portion. A spring member releasably interposed between the first wall portion of the support frame member resiliently holds the heat-frangible element against the second wall portion of the support frame member, and overlies and blocks the opening in the first wall portion.
Representatively, the fluid within the fluid-filled glass bulb may be peanut oil, mineral oil or an assembly lubricant such as Proeco 46 assembly lubricant as manufactured and sole by Cognis Corporation, 8150 Holton Drive, Florence, Ky. 41042. Other suitable fluids could alternatively be utilized if desired.
An open-topped pan structure is supported beneath the arrestor plate and has a bottom wall opening beneath which a shutoff damper is supported in an open position, and is resiliently biased upwardly toward a closed position in which the damper shuts off combustion air flow to the combustion chamber. The temperature sensing structure includes a rod having a first end portion anchored to the damper for movement therewith, and a second end portion extending upwardly through the arrestor plate rod opening and the overlying openings in the base wall of the base frame member and the first wall portion of the support frame member and resiliently bearing against the spring member carried by the support frame member.
The rod is thus prevented from upward movement by the frame spring and frangible element and in turn blocks the damper from moving upwardly toward its closed position. When the set point temperature of the temperature sensing structure is reached within the combustion chamber, the frangible element shatters, thereby freeing the rod for upward movement through the base frame/support frame structure. This, in turn, permits the upwardly biased damper to be forced upwardly to its closed position, with the frame spring member being ejected from the overall frame structure by the upwardly moving rod.